Salazar's also likely getting some heat from back home. He was elected on a pledge to be a moderate Democrat and to oppose 'Rat filibusters of judicial nominees. But instead of being the moderate he claimed to be, he's been a far left partisan since taking office. I think this is generating some heat from the voters back home so he needed to cast a vote for a conservative nominee to cool things down a little. As you noted, he also likely knew Pryor personally so this was a good vote for Salazar to defect from the party line.
I think the filibuster deal got him cover for that campaign statement. I don't think he ever voted to filibuster any judges. And he would be someone who could personally know Pryor.